In some cases, gentle sparging of pure oxygen (or air) is possible if the cells are not too sensitive and serum content of the medium is low. Sparging is, in these cases, done via a sintered sparger.
For microcarrier cultures, sparging can be done inside a rotating sieve cage. The sieve mesh allows the medium to pass and prevents the microcarriers (with attached cells) from coming into contact with the gas bubbles. Rotation of the sieve prevents clogging.
Oxygenation can also be achieved by diffusion through membranes made from e.g. silicone.